A novel method to analyse MR pulmonary images based on the Phase-Resolved Functional Lung MRI (PREFUL) technique
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Abstract
Many pulmonary diseases, such as cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD) or asthma are disrupting the lung perfusion/ventilation ratio. Therefore, monitoring it gives a good overview on the evolution of the disease. There are several imaging modalities to assess the ventilation and perfusion, but they either use ionizing radiation, are expensive, uncomfortable or pose the risk of allergic reactions. Fourier decomposition MRI is a radiation and contrast free technique to image the lungs that is also used while the patient can breathe freely. It is based on the separation of the ventilation and perfusion signals, according to their frequency. Built on top of this is the Phase-Resolved Functional Lung MRI (PREFUL) which allows for the reconstruction of the breathing and cardiac cycle based on the phases of the acquired signal. The present study analysed different methods to extract the phase, to obtain the ventilation and perfusion maps and to threshold and detect the defects. It was found that the methods based on sine fitting and Morlet wavelet are the most promising, with the latter having the advantages of a variable window size and frequency. The most promising threshold for perfusion is the 75th percentile * 0.6 and for ventilation the 90th percentile * 0.4. Despite not correlating very well with the established methods, PREFUL analysis could still be useful in comparing different patients and tracking the progress of lung diseases.